Puff---------Linux Bash Scripting---if supplement and for loop

BASH: Procedural programming, in order to accomplish more complex tasks, support sequential execution, select execution, loop execution

Sequential execution: From left to right, execute command sequentially.

Select Execute: Select to execute a different code fragment based on the execution status result of the condition (condition).

Loop execution: Determines whether to enter the loop according to the execution status result of the condition (condition).

Condition

Ture: Indicates a condition status result of 0

False: Indicates conditional execution status result not 0

If

Single-branch, dual-branch, multi-branch, nested IF statements

1, single branch structure if condition; Then If-turefi2, double branching structure if condition; Then If-tureelse if-falsefi3, multi-branch structure if condition; then if-tureelif condition; then if-tureelif condition; Then if-ture ... else all-falsefi4, nested if statement if condition; Then if condition; Then if-ture fifiif condition; Then if condition; Then if-ture fielse if condition; Then If-ture fi fi

For

List loops

Format

1, format a for variable name in the list; Do loop body done2, format two for variable name in list do loop Hugh Done3, format three, command line for variable name in list; Do loop body; Done

List representation methods

1, give out table 2, {first. Mantissa}, for example 1 to 100 for "{1..100}" 3, Command Reference: 1) $ (ls DIR) 2) $ (expr [step]] mantissa), for example 1 to 100 is represented as "$ (1 1 100)" 4, wildcard, Glob. For example, the absolute path of all files and directories in the sub-directory under the/var directory. /VAR/*5, variable reference. $* all parameters passed to the script, as a whole. [email protected] All parameters passed to the script, each independent

Script format

#!/bin/bash# version:major.minor.release# author:# Desc:

Script Syntax detection

# bash-n File.sh

Debug scripts

# bash-x File.sh

Log script exit status code

Inteval=$? (Variable reference implementation Assignment)

User Mailbox Location

/var/mail

Define the type of the variable

Integral type: # declare-i var

Defining environment variables

# env var# declare-x var# export var

Defining read-only variables

# declare-r var# readonly var

Show local and environment variables

# set

Display environment variables

# export# env# printenv

Show read-only variables

# readonly-p

Example one: interactively give a file path to determine the type of file

#!/bin/bash# version:0.0.1# author:lcc.org# description:testingread-t 5-p ' Enter a file path: ' Filenameif [-Z ' $file Name "]; Thenecho "Enter a file path" Exit 1fiif [!-e $filename]; Thenecho "No such file." Exit 2fiif [-f $filename]; Thenecho "Common file." elif [-H $filename]; Thenecho "symbolic file." elif [-D $filename]; Thenecho "Directory." else echo "other type." Fi

Example two: Add 10 users, User1,,.... user10, password with the user name (only root can change the password).

* * Only root can change password * *

1, list, give the #!/bin/bash# version: 0.0.2# author: lcc.org# description: add  directly user# #避免执行命令的用户非root用户, a non-root user cannot change the password. if [  $UID  -ne 0 ]; then  echo  "Only root."   exit 1fi# #以给出列表的方式, cycle. When the list cycle is complete, the loop ends For i in user1 user2 user3 user4 user5 user6 user7  user8 user9 user10; do  ##  determine if the user exists.   if id  $i  &> /dev/null; then    ##  What does it mean when the condition is true when the execution status result is 0 o'clock?     echo  "$i  exist"   else         ##  Add user if ! useradd  $i  2> /dev/null; then  ## when the user does not exist   Add unsuccessful when,  in combination, reverse the command or test condition.   echo  "$i  is outside the law" else  ##  user name, Normal, can add the user normally, You can add a password to it          &Nbsp;echo  "$i"  | passwd --stdin  $i  > /dev/null 2>&1           ##  numeric test adds the execution status result of the password.   if [ $? -ne 0 ]; then    ##  results are not 0, indicating unsuccessful execution     echo  "Password is not legal"   fi     Fi  fidone2, {1..10}#!/bin/bash# version: 0.0.3# author: lcc.org#  description: {} represents the list [ !  $UID  -eq 0 ] && echo  "only  Root. "   && exit 1for i in {1..10}do  id user$i & > /dev/null  if [ $? -eq 0 ]; then    echo   "User$i exist"   else    useradd user$i 2> /dev/null [ $? -ne 0 ] && echo  "Username is not legal"  && continueecho  "User${i}"  |  passwd --stdin user${i} &> /dev/null[ $? -ne 0 ] & & echo  "Password is not legal" echo  "add user user$i finished"   fidone3, command Reference #!/bin/bash# version: 0.0.4# author: lcc.org# description:   $ (SEQ 10) represents the list [ !  $UID  -eq 0 ] && echo  "only  root. "   && exit 1for i in $ (seq 10) do  id user$i  &> /dev/null  if [ $? -eq 0 ]; then     echo  "User$i exist"   else    useradd user$i 2 > /dev/null[ $? -ne 0 ] && echo  "Username is not  legal " && continueecho  "User${i}"  | passwd --stdin user${i} &> / dev/null[ $? -ne 0 ] && echo  "Password is not legal" echo  "add user user$i finished"   fidone4, special variable #!/bin/bash# version:  0.0.5# author: lcc.org# description: $*,[email protected] represents the list [ !  $UID   -eq 0 ] && echo  "Only root."   && exit 1for i in $*do  id  $i  &>  /dev/null  if [ $? -eq 0 ]; then    echo  "$i  exist "  else    useradd  $i  2> /dev/null[ $? - ne 0 ] && echo  "Username is not legal"  &&  continueecho  "${i}"  | passwd --stdin ${i} &> /dev/null[ $? -ne 0 ] && echo  "Password  is not legal "echo " add user  $i  finished "  fidone

Example three: Determine the type of each file in the/var/directory

Method One #!/bin/bash# version: 0.0.6# author: lcc.org# description: file typefor  i in /var/*; do  if [ -f  $i  ]; then  echo   "Common file."   elif [ -L  $i  ]; then  echo  "Symbolic file."   elif [ -d  $i  ]; then  echo  "Directory."   else    echo  "Other type"   fidone method two:#!/bin/bash#  Version: 0.0.7# author: lcc.org# description: galaxy cd /varfor i  in $ (Ls /var); do  if [ -f  $i  ]; then     echo  "Common file."   elif [ -L  $i  ]; then    echo  "Symbolic file ."   elif [ -d  $i  ]; then    echo  "DirectOry. "   else    echo  "Other type"   fidone method three:#!/bin/bash#  version: 0.0.8# author: lcc.org# description: add dirfor i in $ ( Ls /var)  doif [ -f /var/$i  ]; thenecho  "Common file" elif [  -l /var/$i  ]; thenecho  "Symbolic file" elif [ -d /var/$i  ];  thenecho  "Directory" elseecho  "Other type" Fidone

Example four: How many listen are in the establish State under the TCP protocol, and how many have several states

Method One: #!/bin/bash# version: 0.0.9# author: lcc.org# description: statustcpdeclare  -i listen=0declare -i established=0declare -i other=0for i in $ ( netstat -tan | grep  ' ^tcp\> '  | tr -s  '   '  | cut  -d '   '  -f6); doif [  "$i"  ==  "LISTEN"  ]; thenlet listen++elif  [  "$i"  ==  "established"  ]; thenlet established++elselet other++ fidoneecho -e  "listen statu:  $listen \nestablished statu:  $established \nother  status:  $other \ntotal type: $ (netstat -tan | grep  ' ^tcp\> '  |  tr -s  '   '  | cut -d '   '  -f6 | sort -u |  Wc -l) "Method two:# netstat -tan | grep  ' ^tcp\> '  | awk -v fs= '   '   ' {array[$NF]++}end{for (I in array) {Print i,array[i]}} ' listen 12close_wait 1established 3 

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Puff---------Linux Bash Scripting---if supplement and for loop